The present invention relates to a hydraulic brake system having: (1) anti-lock control and/or traction slip control, (2) an electric-motor-driven hydraulic pump for auxiliary pressure supply during a controlled braking operation and during a traction slip control operation by means of brake management, and (3) an electronic control unit for controlling the auxiliary pressure and for modulating or controlling the braking pressure in the wheel brakes of the controlled wheels in dependence on the rotational behavior of the wheels and/or on signals representing the proper operation of the brake system and of the electronic elements or pointing out malfunctions.
Hydraulic brake systems that are known and provided with electronic anti-lock control and traction slip control are equipped with a one-circuit or multi-circuit hydraulic pump for auxiliary pressure supply. Usually, electric-motor-driven pumps are used that are turned on by the associated electronic control unit upon the onset of control. The hydraulic energy consumption varies very much depending on the control operation and control phase. The nominal capacity of the motor-and-pump unit, of course, is arranged to handle the maximum demand that may appear in certain situations during an anti-lock control operation. As regards traction slip control by means of brake management, where the pump is to deliver the pressure for the application of the brake, less energy and less hydraulic pressure, in principle, are needed as compared with anti-lock control. For cost reasons, the same unit is used for anti-lock control and traction slip control, although a smaller, less potential motor-and-pump unit would be sufficient for traction slip control.
The noise developed upon the onset of control and caused by the turning-on or rather by the operation of the hydraulic pump, however, is felt as a disturbance, namely a reduction in driving comfort, during a traction slip control operation.